我有这样的表达：Expression<Func<MyEntity, bool>> exp = x => x.FirstName == "Jonas";该表达式被传输到另一个不具有类型的应用程序MyEntity。为了能够执行表达式，我尝试将其中的类型替换为ExpandoObject使用ExpressionVistor. public class ReplaceToExpandoVisitor : ExpressionVisitor { ParameterExpression _parameter; private Type _targetType = typeof(ExpandoObject); public ReplaceToExpandoVisitor(ParameterExpression p2) { _parameter = p2; } protected override Expression VisitParameter(ParameterExpression node) { return _parameter; } protected override Expression VisitMember(MemberExpression node) { if (node.Member.MemberType != System.Reflection.MemberTypes.Property) throw new NotSupportedException(); var memberName = node.Member.Name; var propBinder = Binder.GetMember(CSharpBinderFlags.None, memberName, GetType(), new[] { CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null) }); var inner = Visit(node.Expression); // this is the right way, right? var exp2 = Expression.Dynamic(propBinder, typeof(object), inner); // I need to convert it right? Otherwise it will be of type object? var propGetExpression = Expression.Convert(exp2, node.Type); return propGetExpression; } }然而，该表达式在执行时返回 false。所以我想我没有正确访问 Expandoobject 中的“属性”。有人可以解释我做错了什么吗？
1 回答
翻阅古今
TA贡献1780条经验 获得超5个赞
我认为你使用活页夹使事情变得过于复杂。ExpandoObject实现IDictionary<string, object>接口，因此您可以替换x => x.FirstName == "Jonas"为x => x["FirstName"] == "Jonas"哪个应该更容易。另外，您必须重写VisitLambda, 来修改类型参数，否则转换将失败。
这是示例代码：
public class ReplaceToExpandoVisitor<TSource> : ExpressionVisitor
{
private static readonly PropertyInfo ItemProperty = typeof(IDictionary<string, object>).GetProperty("Item");
private readonly ParameterExpression _targetParameter = Expression.Parameter(typeof(ExpandoObject));
protected override Expression VisitLambda<T>(Expression<T> node)
{
var body = this.Visit(node.Body);
var parameters = node.Parameters.Select(this.Visit).Cast<ParameterExpression>();
return Expression.Lambda(body, parameters);
}
protected override Expression VisitParameter(ParameterExpression node)
{
if (node.Type == typeof(TSource))
{
return this._targetParameter;
}
return node;
}
protected override Expression VisitMember(MemberExpression node)
{
if (node.Member.MemberType != MemberTypes.Property)
{
throw new NotSupportedException();
}
string memberName = node.Member.Name;
return Expression.Convert(
Expression.Property(
this.Visit(node.Expression),
ItemProperty,
Expression.Constant(memberName)
),
((PropertyInfo)node.Member).PropertyType
);
}
}
用法：
Expression<Func<MyEntity, bool>> exp = x => x.FirstName == "Jonas";
Expression<Func<ExpandoObject, bool>> exp2 = (Expression<Func<ExpandoObject, bool>>) new ReplaceToExpandoVisitor<MyEntity>().Visit(exp);
dynamic obj = new ExpandoObject();
obj.FirstName = "Jonas";
bool result = exp2.Compile().Invoke(obj);
- 1 回答
- 0 关注
- 74 浏览
添加回答
举报
0/150
提交
取消